The present invention relates to a supply pump for fuel injection into an internal combustion engine. More particularly, the invention relates to a supply pump with pumping plungers which are retained by sliding shoes or a cage.
One type of conventional fuel supply pump has plungers which reciprocate radially in corresponding pumping bores. As each plunger moves toward a filling position, fuel is drawn into the pumping bore. As the plunger moves toward a pumping position, fuel at an elevated pressure is discharged from the pumping bore. The plungers may be internally or externally driven. In an internally driven supply pump a rotating drive member periodically actuates the radially inner end of each plunger outwardly. In this type of pump, fuel is discharged from the bore on the radial outward stroke of the plunger and drawn into the bore on the radial inward stroke of the plunger. Thus the filling position is the radially innermost plunger position and the discharge position is the radially outermost plunger position. The converse arrangement is present in an externally driven supply pump, which has pumping plungers actuated at their radially outer end (e.g., by a rotating annular cam) and therefore a radially inwardly discharge stroke and a radially outwardly filling stroke. In either pump type, the rotary motion of the drive member is converted to linear motion of the plungers for movement to the pumping position. Because the plunger is not attached to the eccentric drive or cam, a spring is used to bias the plunger back toward the filling position. In the conventional fuel supply pump, each plunger is biased and returned to its filling position by its own return spring independently of the other plungers.
Conventionally, a sliding shoe is interposed between the plunger and drive member to aid in conversion of the rotary drive member motion to linear plunger motion. The shoes must be maintained in essentially constant contact with both the drive member and the plunger end. This is usually accomplished via an independent spring bias for each shoe and a pivotable connection between the shoe and plunger. Typically, each plunger and its respective shoe is biased by the same spring. The pivotable connection between the plunger and shoe presents problems in manufacture and assembly. Conventionally, it is difficult to find a shoe material with adequate wear resistance yet still ductile enough to allow the shoe to be formed around a plunger end to capture the plunger. It is also difficult to mechanically form the sliding shoe around the plunger captured end while achieving the optimum retentive fit between these components. Finally, assembly of the sliding shoe/plunger sub-assembly into the fuel pump bore is difficult and can only be done manually.
More efficient space utilization, higher pump efficiency and improved sliding surface lubrication can be achieved by eliminating the conventional coil return springs and dynamically connecting all of the sliding shoes or all of the plungers. In particular, a pivotable connection between the plunger and the shoe and desmodromic drive of these reciprocating members by an energizing ring or retainer cage, make spring elimination and the previously mentioned benefits possible.